1. Related Art
Among the conventional methods for glazing ceramic articles, there are known such methods as are disclosed in JP Patent Kokoku JP-B-51-37658, JP Patent Kokoku JP-B-57-27061, JP-Patent Kokai JP-A-5-262582 and JP patent kokai JP-A-5-310485.
The JP Patent Kokoku JP-B-51-37658 is concerned with a technique for decorating a ceramic ware consisting in coating the surface of the ceramic article with a water-repellent agent containing an inorganic pigment and firing the resulting mass for fixing the pigment. By way of a preferred embodiment, there is described a technique of printing a water-repellent agent containing a pigment for underglazing for ceramic articles by a screen printing method for providing a water-repellent surface, further applying a dark-green transparent glaze thereon and firing the resulting mass to provide a colored surface having the water-repellent surface free from the risk of deposition of the glaze and also having the water-repellent surface colored with the pigment as a result of firing.
The JP Patent Kokoku JP-B-57-27061 is concerned with a decorating method consisting in (i) forming a contour pattern on a substrate surface with an oily pigment-containing silicone oil, (ii) painting a mixture of a glaze, a pigment and a water-soluble silicone water-repellent agent within the contour pattern, and (iii) brushing a common underglazing coloring agent on a dried surface, followed by application of a glaze and firing. The oily pigment exhibits sufficient water repellency so that the mixture is repelled and applied in a state of being swollen (or reliefed) in the contour pattern.
The JP Patent Kokai JP-A-5-262582 is concerned with a method for producing a pottery product consisting in partially coating the base surface with a water absorption speed adjusting agent designed for retarding the water absorption speed at the time of glazing prior to the glazing step, then applying the glaze on the substrate surface for forming a glaze layer and firing the resulting mass. It is stated in the Kokai-Publication that, while the moisture of the glaze applied tends to be easily absorbed by the substrate to facilitate deposition of the glaze in the substrate surface portion not coated with the water absorption speed adjustment agent, while the moisture of the glaze coated is not liable to be absorbed on the base surface portion coated with the adjustment agent so that the glaze is hardly deposited to reduce the thickness in this substrate surface portion thus forming a glaze layer having an irregular surface as a whole.
In the above Kokai-Publication, triethanolamine, polyvinyl alcohol, carboxymethyl cellulose, ethyl alcohol and ethylene glycol are stated as examples of the water absorption adjustment agent.
The JP Patent Kokai JP-A-5-310485 states that a fine irregular ceramic pattern is formed by taking advantage of the fact that a patterned printing pattern (decoration) by the water-repellent resin or a patterned printing (decoration) pattern prior to firing containing a fired pigment exhibit the repellent operation against the aqueous glaze, and by producing a glaze layer in which the portion in register with the patterned printing pattern is devoid of a pattern.
2. Discussion on the Related Art
However, according to the eager investigation toward the present invention there have been encountered following problems. With the conventional method for producing a ceramic article or with the conventional glazing method, it has been extremely difficult to produce a ceramic article having a relief pattern with attractive appearance, that is a ceramic article having a sufficient glaze thickness and exhibiting a clear irregular relief pattern.
In the production process for ceramic articles, the glaze is applied to a pre-set thickness sufficient to achieve the objectives of preventing the liquid or the gas from being permeated through the substrate, realizing the beautiful appearance inclusive of luster and color, and increasing the mechanical strength of the substrate. In general, the thickness of the fired glaze layer after firing is on the order of at least 0.3 to 0.4 mm.
However, if a relief pattern is formed on the substrate for affording more beautiful appearance to the ceramic articles, and if the glaze is applied in the same way as when there is no relief pattern on the substrate, an abundant quantity of glaze slurry is accumulated in recessed (engraved) portions of the relief surface than in other portions thus refilling the recesses to flatten out the relief surface.
The result is that the relief pattern of the relief surface becomes blurred such that it becomes extremely difficult to produce a ceramic article having a well-defined/clear-cut relief pattern of sufficient depth on the as-fired surface.
In particular, if the relief surface is machined more intricately or finely for realizing a more attractive surface, defects tend to be produced in a boundary area between the relief surface and the planar non-relief surface. In particular, defects in appearance, such as non-glazed portions like pinholes or sagging of the glaze slurry tend to be produced.
Meanwhile, if the glaze slurry is applied on the entire substrate surface, to a thickness not completely filling out the recesses on the relief surface, the glaze slurry applied to the base portion not taking part in forming the relief pattern becomes thin in thickness, such that the above objectives may not be achieved.